The Caleufú is a modest, clear-running river running east from the confluence of the Filo Hua Hum and Meliquina, south-east of San Martín de los Andes, to join the Collón Curá, alluvial gravel underfoot and enough structure — undercuts, seams, back-eddies — to hold fish without ever feeling crowded. It suits a dry-dropper approach well: a buoyant attractor trailing a Pheasant Tail or Hare's Ear picks up both the riser working a hatch and the fish holding deeper that won't commit to the surface. Prince Nymph and Copper John patterns earn their place in faster runs where a little more weight is needed to get down quickly. Access is generally open and locals fish it hard, so timing and a willingness to walk past the first pool pay off. It's the kind of unglamorous, workmanlike river that rewards an angler who reads water carefully rather than one chasing a famous name.

• Alluvial